Virtualization - Nov 2008 - [patch 0/4] [RFC] Another proportional weight IO controller

Hi,

If you are not already tired of so many io controller implementations, here
is another one.

This is a very eary very crude implementation to get early feedback to see
if this approach makes any sense or not.

This controller is a proportional weight IO controller primarily
based on/inspired by dm-ioband. One of the things I personally found little
odd about dm-ioband was need of a dm-ioband device for every device we want
to control.  I thought that probably we can make this control per request
queue and get rid of device mapper driver. This should make configuration
aspect easy.

I have picked up quite some amount of code from dm-ioband especially for
biocgroup implementation.

I have done very basic testing and that is running 2-3 dd commands in different
cgroups on x86_64. Wanted to throw out the code early to get some feedback.

More details about the design and how to are in documentation patch.

Your comments are welcome.

Thanks
Vivek

--

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On Thu, 2008-11-06 at 10:30 -0500, vgoyal at redhat.com
wrote:
> Hi,
> 
> If you are not already tired of so many io controller implementations, here
> is another one.
> 
> This is a very eary very crude implementation to get early feedback to see
> if this approach makes any sense or not.
> 
> This controller is a proportional weight IO controller primarily
> based on/inspired by dm-ioband. One of the things I personally found little
> odd about dm-ioband was need of a dm-ioband device for every device we want
> to control.  I thought that probably we can make this control per request
> queue and get rid of device mapper driver. This should make configuration
> aspect easy.
> 
> I have picked up quite some amount of code from dm-ioband especially for
> biocgroup implementation.
> 
> I have done very basic testing and that is running 2-3 dd commands in
different
> cgroups on x86_64. Wanted to throw out the code early to get some feedback.
> 
> More details about the design and how to are in documentation patch.
> 
> Your comments are welcome.
please include

QUILT_REFRESH_ARGS="--diffstat --strip-trailing-whitespace"

in your environment or .quiltrc

I would expect all those bio* files to be placed in block/ not mm/

Does this still require I use dm, or does it also work on regular block
devices? Patch 4/4 isn't quite clear on this.

On Thu, 2008-11-06 at 11:57 -0500, Rik van Riel wrote:
> Peter Zijlstra wrote:
> 
> > The only real issue I can see is with linear volumes, but those are
> > stupid anyway - non of the gains but all the risks.
> 
> Linear volumes may well be the most common ones.
> 
> People start out with the filesystems at a certain size,
> increasing onto a second (new) disk later, when more space
> is required.
Are they aware of how risky linear volumes are? I would discourage
anyone from using them.

On Thu, Nov 06, 2008 at 06:11:27PM +0100, Peter Zijlstra
wrote:
> On Thu, 2008-11-06 at 11:57 -0500, Rik van Riel wrote:
> > Peter Zijlstra wrote:
> > 
> > > The only real issue I can see is with linear volumes, but those
are
> > > stupid anyway - non of the gains but all the risks.
> > 
> > Linear volumes may well be the most common ones.
> > 
> > People start out with the filesystems at a certain size,
> > increasing onto a second (new) disk later, when more space
> > is required.
> 
> Are they aware of how risky linear volumes are? I would discourage
> anyone from using them.
In what way are they risky?

Cheers,

Dave.
-- 
Dave Chinner
david at fromorbit.com

vgoyal at redhat.com wrote:
> Hi,
> 
> If you are not already tired of so many io controller implementations, here
> is another one.
> 
> This is a very eary very crude implementation to get early feedback to see
> if this approach makes any sense or not.
> 
> This controller is a proportional weight IO controller primarily
> based on/inspired by dm-ioband. One of the things I personally found little
> odd about dm-ioband was need of a dm-ioband device for every device we want
> to control.  I thought that probably we can make this control per request
> queue and get rid of device mapper driver. This should make configuration
> aspect easy.
> 
> I have picked up quite some amount of code from dm-ioband especially for
> biocgroup implementation.
> 
> I have done very basic testing and that is running 2-3 dd commands in
different
> cgroups on x86_64. Wanted to throw out the code early to get some feedback.
> 
> More details about the design and how to are in documentation patch.
> 
> Your comments are welcome.
  Which kernel version is this patch set based on?
> 
> Thanks
> Vivek
> 
-- 
Regards
Gui Jianfeng

On Thu, 06 Nov 2008 10:30:24 -0500
vgoyal at redhat.com wrote:
> 
> o biocgroup functionality.
> o Implemented new controller "bio"
> o Most of it picked from dm-ioband biocgroup implementation patches.
> 
page_cgroup implementation is changed and most of this patch needs rework.
please see the latest one. (I think most of new characteristics are useful
for you.)

One comment from me is
=> +struct page_cgroup {
> +	struct list_head lru;		/* per cgroup LRU list */
> +	struct page *page;
> +	struct mem_cgroup *mem_cgroup;
> +	int flags;
> +#ifdef CONFIG_CGROUP_BIO
> +	struct list_head blist;		/* for bio_cgroup page list */
> +	struct bio_cgroup *bio_cgroup;
> +#endif
> +};
=
this blist is too bad. please keep this object small...

Maybe dm-ioband people will post his own new one. just making use of it is an
idea.

Thanks,
-Kame

On Fri, 2008-11-07 at 11:41 +1100, Dave Chinner wrote:
> On Thu, Nov 06, 2008 at 06:11:27PM +0100, Peter Zijlstra wrote:
> > On Thu, 2008-11-06 at 11:57 -0500, Rik van Riel wrote:
> > > Peter Zijlstra wrote:
> > > 
> > > > The only real issue I can see is with linear volumes, but
those are
> > > > stupid anyway - non of the gains but all the risks.
> > > 
> > > Linear volumes may well be the most common ones.
> > > 
> > > People start out with the filesystems at a certain size,
> > > increasing onto a second (new) disk later, when more space
> > > is required.
> > 
> > Are they aware of how risky linear volumes are? I would discourage
> > anyone from using them.
> 
> In what way are they risky?
You loose all your data when one disk dies, so your mtbf decreases with
the number of disks in your linear span.

And you get non of the benefits from having multiple disks, like extra
speed from striping, or redundancy from raid.

Therefore I say that linear volumes are the absolute worst choice.

On Fri, Nov 07, 2008 at 10:36:50AM +0800, Gui Jianfeng
wrote:
> vgoyal at redhat.com wrote:
> > Hi,
> > 
> > If you are not already tired of so many io controller implementations,
here
> > is another one.
> > 
> > This is a very eary very crude implementation to get early feedback to
see
> > if this approach makes any sense or not.
> > 
> > This controller is a proportional weight IO controller primarily
> > based on/inspired by dm-ioband. One of the things I personally found
little
> > odd about dm-ioband was need of a dm-ioband device for every device we
want
> > to control.  I thought that probably we can make this control per
request
> > queue and get rid of device mapper driver. This should make
configuration
> > aspect easy.
> > 
> > I have picked up quite some amount of code from dm-ioband especially
for
> > biocgroup implementation.
> > 
> > I have done very basic testing and that is running 2-3 dd commands in
different
> > cgroups on x86_64. Wanted to throw out the code early to get some
feedback.
> > 
> > More details about the design and how to are in documentation patch.
> > 
> > Your comments are welcome.
> 
>   Which kernel version is this patch set based on?
> 
2.6.27

Thanks
Vivek

On Fri, Nov 07, 2008 at 11:50:30AM +0900, KAMEZAWA Hiroyuki
wrote:
> On Thu, 06 Nov 2008 10:30:24 -0500
> vgoyal at redhat.com wrote:
> 
> > 
> > o biocgroup functionality.
> > o Implemented new controller "bio"
> > o Most of it picked from dm-ioband biocgroup implementation patches.
> > 
> page_cgroup implementation is changed and most of this patch needs rework.
> please see the latest one. (I think most of new characteristics are useful
> for you.)
> 
Sure I will have a look.
> One comment from me is
> => > +struct page_cgroup {
> > +	struct list_head lru;		/* per cgroup LRU list */
> > +	struct page *page;
> > +	struct mem_cgroup *mem_cgroup;
> > +	int flags;
> > +#ifdef CONFIG_CGROUP_BIO
> > +	struct list_head blist;		/* for bio_cgroup page list */
> > +	struct bio_cgroup *bio_cgroup;
> > +#endif
> > +};
> => 
> this blist is too bad. please keep this object small...
> 
This is just another connecting element so that page_cgroup can be on another
list also. It is useful in making sure that IO on all the pages of a bio
group has completed beofer that bio cgroup is deleted.
> Maybe dm-ioband people will post his own new one. just making use of it is
an idea.
Sure, I will have a look when dm-ioband people post new version of patch
and how they have optimized it further.

Thanks
Vivek

vgoyal at redhat.com wrote:

Hi vivek,

I think bio_group_controller() need to be exported by EXPORT_SYMBOL()

-- 
Regards
Gui Jianfeng

Hi,

From: vgoyal at redhat.com
Subject: [patch 0/4] [RFC] Another proportional weight IO controller 
Date: Thu, 06 Nov 2008 10:30:22 -0500
> Hi,
> 
> If you are not already tired of so many io controller implementations, here
> is another one.
> 
> This is a very eary very crude implementation to get early feedback to see
> if this approach makes any sense or not.
> 
> This controller is a proportional weight IO controller primarily
> based on/inspired by dm-ioband. One of the things I personally found little
> odd about dm-ioband was need of a dm-ioband device for every device we want
> to control.  I thought that probably we can make this control per request
> queue and get rid of device mapper driver. This should make configuration
> aspect easy.
> 
> I have picked up quite some amount of code from dm-ioband especially for
> biocgroup implementation.
> 
> I have done very basic testing and that is running 2-3 dd commands in
different
> cgroups on x86_64. Wanted to throw out the code early to get some feedback.
> 
> More details about the design and how to are in documentation patch.
> 
> Your comments are welcome.
Do you have any benchmark results?
I'm especially interested in the followings:
- Comparison of disk performance with and without the I/O controller patch.
- Put uneven I/O loads. Processes, which belong to a cgroup which is
  given a smaller weight than another cgroup, put heavier I/O load
  like the following.

     echo 1024 > /cgroup/bio/test1/bio.shares
     echo 8192 > /cgroup/bio/test2/bio.shares

     echo $$ > /cgroup/bio/test1/tasks
     dd if=/somefile1-1 of=/dev/null &
     dd if=/somefile1-2 of=/dev/null &
     ... 
     dd if=/somefile1-100 of=/dev/null
     echo $$ > /cgroup/bio/test2/tasks
     dd if=/somefile2-1 of=/dev/null &
     dd if=/somefile2-2 of=/dev/null &
     ...
     dd if=/somefile2-10 of=/dev/null &

Thanks,
Ryo Tsuruta

On Wed, Nov 26, 2008 at 6:06 AM, Paolo Valente <paolo.valente at
unimore.it> wrote:
> Fabio and I are a little bit worried about the fact that the problem
> of working in the time domain instead of the service domain is not
> being properly dealt with.  Probably we did not express ourselves very
> clearly, so we will try to put in more practical terms.  Using B-WF2Q+
> in the time domain instead of using CFQ (Round-Robin) means introducing
> higher complexity than CFQ to get almost the same service properties
> of CFQ.  With regard to fairness (long term) B-WF2Q+ in the time domain
Are we talking about a case where all the contenders have equal
weights and are continuously backlogged? That seems to be the only
case when B-WF2Q+ would behave like Round-Robin. Am I missing
something here?

I can see that the only direct advantage of using WF2Q+ scheduling is
reduced jitter or latency in certain cases. But under heavy loads,
that might result in request latencies seen by RT threads to be
reduced from a few seconds to a few msec.
> has exactly the same (un)fairness problems of CFQ.  As far as bandwidth
> differentiation is concerned, it can be obtained with CFQ by just
> increasing the time slice (e.g., double weight => double slice).  This
> has no impact on long term guarantees and certainly does not decrease
> the throughput.
>
> With regard to short term guarantees (request completion time), one of
> the properties of the reference ideal system of Wf2Q+ is that, assuming
> for simplicity that all the queues have the same weight, as the ideal
> system serves each queue at the same speed, shorter budgets are completed
> in a shorter time intervals than longer budgets.  B-WF2Q+ guarantees
> O(1) deviation from this ideal service.  Hence, the tight delay/jitter
> measured in our experiments with BFQ is a consequence of the simple (and
> probably still improvable) budget assignment mechanism of (the overall)
> BFQ.  In contrast, if all the budgets are equal, as it happens if we use
> time slices, the resulting scheduler is exactly a Round-Robin, again
> as in CFQ (see [1]).
Can the budget assignment mechanism of BFQ be converted to time slice
assignment mechanism? What I am trying to say here is that we can have
variable time slices, just like we have variable budgets.
>
> Finally, with regard to completion time delay differentiation through
> weight differentiation, this is probably the only case in which B-WF2Q+
> would perform better than CFQ, because, in case of CFQ, reducing the
> time slices may reduce the throughput, whereas increasing the time slice
> would increase the worst-case delay/jitter.
>
> In the end, BFQ succeeds in guaranteeing fairness (or in general the
> desired bandwidth distribution) because it works in the service domain
> (and this is probably the only way to achieve this goal), not because
> it uses WF2Q+ instead of Round-Robin.  Similarly, it provides tight
> delay/jitter only because B-WF2Q+ is used in combination with a simple
> budget assignment (differentiation) mechanism (again in the service
> domain).
>
> [1] http://feanor.sssup.it/~fabio/linux/bfq/results.php
>
> --
> -----------------------------------------------------------
> | Paolo Valente              |                            |
> | Algogroup                  |                            |
> | Dip. Ing. Informazione     | tel:   +39 059 2056318     |
> | Via Vignolese 905/b        | fax:   +39 059 2056199     |
> | 41100 Modena               |                            |
> |     home:  http://algo.ing.unimo.it/people/paolo/       |
> -----------------------------------------------------------
>
>

> From: Nauman Rafique <nauman at google.com>
> Date: Wed, Nov 26, 2008 11:41:46AM -0800
>
> On Wed, Nov 26, 2008 at 6:06 AM, Paolo Valente <paolo.valente at
unimore.it> wrote:
> > Fabio and I are a little bit worried about the fact that the problem
> > of working in the time domain instead of the service domain is not
> > being properly dealt with.  Probably we did not express ourselves very
> > clearly, so we will try to put in more practical terms.  Using B-WF2Q+
> > in the time domain instead of using CFQ (Round-Robin) means
introducing
> > higher complexity than CFQ to get almost the same service properties
> > of CFQ.  With regard to fairness (long term) B-WF2Q+ in the time
domain
> 
> Are we talking about a case where all the contenders have equal
> weights and are continuously backlogged? That seems to be the only
> case when B-WF2Q+ would behave like Round-Robin. Am I missing
> something here?
> 
It is the case with equal weights, but it is really a common one.

> I can see that the only direct advantage of using WF2Q+ scheduling is
> reduced jitter or latency in certain cases. But under heavy loads,
> that might result in request latencies seen by RT threads to be
> reduced from a few seconds to a few msec.
> 
> > has exactly the same (un)fairness problems of CFQ.  As far as
bandwidth
> > differentiation is concerned, it can be obtained with CFQ by just
> > increasing the time slice (e.g., double weight => double slice). 
This
> > has no impact on long term guarantees and certainly does not decrease
> > the throughput.
> >
> > With regard to short term guarantees (request completion time), one of
> > the properties of the reference ideal system of Wf2Q+ is that,
assuming
> > for simplicity that all the queues have the same weight, as the ideal
> > system serves each queue at the same speed, shorter budgets are
completed
> > in a shorter time intervals than longer budgets.  B-WF2Q+ guarantees
> > O(1) deviation from this ideal service.  Hence, the tight delay/jitter
> > measured in our experiments with BFQ is a consequence of the simple
(and
> > probably still improvable) budget assignment mechanism of (the
overall)
> > BFQ.  In contrast, if all the budgets are equal, as it happens if we
use
> > time slices, the resulting scheduler is exactly a Round-Robin, again
> > as in CFQ (see [1]).
> 
> Can the budget assignment mechanism of BFQ be converted to time slice
> assignment mechanism? What I am trying to say here is that we can have
> variable time slices, just like we have variable budgets.
> 
Yes, it could be converted, and it would do in the time domain the
same differentiation it does now in the service domain.  What we would
lose in the process is the fairness in the service domain.  The service
properties/guarantees of the resulting scheduler would _not_ be the same
as the BFQ ones.  Both long term and short term guarantees would be
affected by the unfairness given by the different service rate
experienced by the scheduled entities.

> >
> > Finally, with regard to completion time delay differentiation through
> > weight differentiation, this is probably the only case in which
B-WF2Q+
> > would perform better than CFQ, because, in case of CFQ, reducing the
> > time slices may reduce the throughput, whereas increasing the time
slice
> > would increase the worst-case delay/jitter.
> >
> > In the end, BFQ succeeds in guaranteeing fairness (or in general the
> > desired bandwidth distribution) because it works in the service domain
> > (and this is probably the only way to achieve this goal), not because
> > it uses WF2Q+ instead of Round-Robin.  Similarly, it provides tight
> > delay/jitter only because B-WF2Q+ is used in combination with a simple
> > budget assignment (differentiation) mechanism (again in the service
> > domain).
> >
> > [1] http://feanor.sssup.it/~fabio/linux/bfq/results.php
> >
> > --
> > -----------------------------------------------------------
> > | Paolo Valente              |                            |
> > | Algogroup                  |                            |
> > | Dip. Ing. Informazione     | tel:   +39 059 2056318     |
> > | Via Vignolese 905/b        | fax:   +39 059 2056199     |
> > | 41100 Modena               |                            |
> > |     home:  http://algo.ing.unimo.it/people/paolo/       |
> > -----------------------------------------------------------
> >
> >